Curved offshore well conductors

ABSTRACT

Apparatus and method for producing hydrocarbons from a subterranean hydrocarbon-bearing formation located beneath the floor of a body of water. A platform structure is installed on the floor over the formation and well conductors are extended down the structure and penetrate into the floor of the body of water. The conductors may include an upper vertical portion, then continually curve downwardly and outwardly through the structure above the floor in a manner maintaining a relatively smooth bore throughout the entire extent of the conductors. The conductors are extended into the floor of the body of water and wells are drilled, via the conductors, down into communication with the formation. Formation fluids are then produced from the formation via the conductors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the drilling of wells offshore; and, moreparticularly, to a method and apparatus for producing hydrocarbons fromsubterranean formations under the ocean floor.

2. Description of the Prior Art

In an attempt to locate new oil fields, an increasing amount of welldrilling has been conducted at offshore locations, such, for example, asoff the coasts of California, Louisiana and Texas, and, more recently,off the coast of Alaska and in the North Sea. Generally, platformstructures are installed on the ocean floor and straight well conductorsare extended from the platform structure some distance below the oceanfloor, providing guidance and support for wells drilled intohydrocarbon-bearing reservoirs.

In order to increase the lateral reach of such well conductors, theseconductors have been slanted from the vertical, as for example, in aU.S. Pat. No. 3,451,493 to Storm. Such conductors are usually extendedlaterally beyond the perimeter of a conventional platform structure at aconsiderable distance above the mudline (e.g., about 100 to 150 feet in250-foot water depth), This condition is undesirable since it results inlong spans of well conductors which are unsupported or which requirefabrication of conductor guides outside of the main framework of theplatform structure. Such an arrangement is both costly and complicated.Further, if such well conductors are to perform as a portion of theplatform structure foundation by providing resistance to lateralmovement, the cost of the outrigged framework is considerably increased.

An alternate type of arrangement in applying such straight-slant typeconductors to deep water conditions is to keep the portion of theconductor which is above the mudline inside the framework of theplatform by crisscrossing them in a vertical plane. The wellhead foreach well conductor is located at the top of the platform structure onone side thereof and the bottom well conductor platform support islocated at the mudline near the opposite side of the platform structure.Such an arrangement requires that a large part of the deck area of theplatform structure be designed to accommodate the required slantdrilling rig since the wellheads are not located together. Unless thelayout of the platform structure is axisymmetric, this latter techniquemay result in an undesirable well conductor reach pattern. Moreover, aspecial slant drilling rig must be used rather than the conventionalstraight rig.

Thus, the disadvantages of such prior art arrangements for increasinghorizontal reach are conductor guides external of the platformstructure, possible interference of conductors with the platformstructure foundation, non-centrally located wellheads, possiblyundesirable well conductor reach patterns, and the need for a specialrig. These disadvantages become especially significant in water deeperthan 200 feet.

SUMMARY OF THE INVENTION

It is an object of this invention to provide apparatus and method fordrilling offshore wells using well conductors having increased lateralreach from platform structures installed on the floor of a body ofwater.

It is a further object of this invention to provide such well conductorswherein the conductors and guides are framed inside of the mainframework of the platform structure.

It is a still further object of this invention to increase the lateralreach of such conductors with the ability to provide any desired patternwith respect to the platform structure, depending upon the reservoir.

It is an even further object of this invention to carry out thetechniques disclosed herein without significantly altering the design oroperation of conventional platform structures and drilling rigs.

These and other objects may be accomplished by installing a platformstructure on the floor of a body of water over a subterraneanhydrocarbon-bearing formation below the floor and extending wellconductors down the structure and beneath the floor of the body ofwater. The conductors may include an upper vertical portion, thencontinually curve downwardly and outwardly through the structure abovethe floor in a manner maintaining a relatively smooth bore throughoutthe entire extent of the conductors. The conductors are extended intothe floor beneath the structure and wells are drilled via the conductorsdown into the formation. Formation fluids are then produced from theformation via the conductors.

In addition to the above mentioned objects, a further purpose inemploying curved conductors is to minimize the possibility ofinadvertently drilling into a previously drilled well. The further apartthe conductors are spread at the bottom of the structure, the lesslikelihood there is of drilling into one wellbore while drilling anotherwell.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical view of a platform structure resting on the floorof a body of water and having well conductors installed thereon inaccordance with the teachings of our invention;

FIG. 2 is a perspective view of the platform structure of FIG. 1 showingwell conductor guides on the structure for accommodating the curvatureof the well conductors in accordance with the teachings of ourinvention; and

FIG. 3 is a vertical, partly graphic, view showing the advantages of theteachings of our invention over conventional prior art verticalriggings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to both FIGS. 1 and 2, a conventional platform structure 10 isshown resting on the floor 11 of a body of water 12. Structure 10includes a generally horizontal work platform 13 thereon supported abovethe water surface 14 by suitable framework 15. Framework 15 preferablyincludes a plurality of legs 16 interconnected by a network ofcross-bracing members 17. The lower ends of legs 16 extend into thefloor 11 and are anchored therein by suitable piles 18. It is to beunderstood that conventional well equipment, such as derricks, drawworks, engines, etc., (not shown) may be installed on work platform 13.

In accordance with our invention, a plurality of well conductors areextended from platform 13 along framework 15 to the floor 11 of the bodyof water 12. For example, six such conductors 19 through 24 are shown inFIGS. 1 and 2 (conductor 22 not being visible in FIG. 1). Thus,conductor 22 may extend substantially vertical with respect to platformstructure 10. However, conductors 19, 20, 21, 23 and 24 extend firstvertically downwardly with respect to platform structure 10 thencontinually curve downwardly and outwardly in any desired pattern asillustrated in FIGS. 1 and 2.

Although only six such well conductors are shown extending from platform13, obviously a plurality of such conductors may be provided, soarranged with respect to platform structure 10 so as to provide anoptimum lateral reach in the desired directions from the structure 10.

The curvature applied to conductors 19, 20, 21, 23 and 24 may beconstant or varying; however, in either case, a smooth bore is providedthroughout substantially the entire extent of the conductors therebypermitting sharper curvatures than may normally be permitted whendrilling into the floor 11. In this manner, the early attainment of highangles of deviation increases the lateral reach of the well conductorswhile retention of conventional vertical drilling techniques ispermitted by having the curved conductors vertical at their top ends.

Preferably, the conductors are supported at intervals along platformstructure 10 by conductor guides 25 (FIG. 2) built into the platformstructure 10 so as to accommodate the curvature of the conductors. Theseguides 25 have been omitted in FIG. 1 for convenience of illustration.As shown in FIG. 2, guides 25 may take the form of ring elements or thelike secured to the legs 16 or framework 15 of platform structure 10 ata plurality of staggered offset locations. These guides 25 provideguidance and support for the conductors. Curvature may be imparted tothe conductors by .[.performing.]. .Iadd.preforming .Iaddend.theconductors and/or by elastically bending the conductors duringinstallation through the series of slightly offset guides 25. Thepreformed or plastically-bent conductors may be used to continuebuilding angle below the bottom conductor guides 25 (generally at themudline or floor 11). Conventional drilling, jetting, driving, or acombination of these techniques may be used to install the conductorsthrough floor 11. Further, the curved well conductor provides continuoussupport for casing and tubing which can be conventionally drilled intocommunication with subterranean reservoir 26 shown schematically in FIG.3. Additionally, conductors 19 through 24 may or may not double aspiling, as is well known in the drilling art, to support platformstructure 10.

Thus, as can be seen in FIG. 3, one of the curved conductors (e.g.,conductor 24) is shown adjacent a conventional prior art "straight"vertical conductor. As can be seen, the lateral reach capability of thewell conductors is increased when such conductors are continually curvedwhen drilled with respect to a single platform structure 10. Thetechniques of our invention are particularly well suited for combinedconditions of deep water (i.e., a water depth or W.D. of between 200 and400 feet or so) and shallow reservoir depth (i.e., a reservoir depth orR.D. of about 5,000 feet more or less). When compared with known priorart techniques, as, for example, the "straight" vertical conductor ofFIG. 3 which is shown as having been driven to 150 foot penetration withthe wellbore deviated horizontally from that point, curved conductor 24,having a moderate curvature of, for example, six degrees every 100 feetor so, nearly doubles the acreage that can be reached from the singleplatform structure 10.

Thus, in drilling wells in accordance with the techniques of ourinvention, a slant rig is not required since the wells may be drilledusing conventional vertical-type equipment. Additional deck space onplatform 13 which may be necessary to move and operate a slant rig isnot required nor is special designing of platform 13 to accommodate sucha rig necessary. Finally, as shown in FIG. 1, conventional wellheadequipment 27 through 31 may be associated with conductors 19, 20, 21, 23and 24 (the equipment associated with conductor 22 not being visible inFIG. 1) for recovering formation fluids produced from the reservoir 26of FIG. 3. This equipment may be clustered in a central location on theplatform 13 of platform structure 10 of the same spacing and shape as isconventionally required for producing formation fluids from "Straight"vertical conductors.

In summary, the curved conductors of our invention may be designed tonearly match or exceed (depending on water depth) the reach capabilityof conventional slant conductors without the inherent disadvantages ofthe latter, i.e., the conductors and guides may be framed inside theplatform structure, the framing at the mudline may economically bedesigned to enable the curved conductor to function as part of theplatform foundation system and so as not to interfere with theinstallation, the well head equipment may be centrally located, and anydesired reach pattern may be achieved. Further, the curved conductorsmay be installed and wells may be drilled using conventionalvertical-type equipment and techniques. For deep water-shallow reservoirconditions, the curved conductor may be installed and operated withoutsignificantly altering the design or operation of the platform from thatwhich is conventionally used for straight-vertical conductors. Thecurved conductors of our invention may be used in combination withstraight vertical conductors to greatly increase the number of wellswhich can be drilled from a single platform structure.

We claim as our invention:
 1. A method for producing hydrocarbons from asubterranean hydrocarbon-bearing formation located beneath the floor ofa body of water, said method comprising the steps of:installing aplatform structure on the floor of said body of water above saidformation; extending at least one well conductor downwardly with respectto said platform structure, then curving said conductor outwardly anddownwardly through said platform structure above the floor of said bodyof water in a manner maintaining a relatively smooth bore throughoutsubstantially the entire extent of said conductor; drilling via saidconductor down through said floor and into fluid communication with saidformation; and producing formation fluids from said formation via saidconductor.
 2. The method of claim 1 wherein the step of curving saidconductor includes the steps of:providing guide means at a plurality ofvertically spaced locations on said platform structure adapted to curvesaid conductor; and extending said conductor into communication withsaid guide means thereby curving said conductor through said guidemeans.
 3. The method of claim 1 wherein the step of extending at leastone well conductor downwardly with respect to said platform structureincludes the step of extending a plurality of well conductors downwardlywith respect to said platform, at least some of said well conductorsbeing extended outwardly and downwardly with respect to said platformstructure in a direction different from that of an adjacent wellconductor in a predetermined pattern with respect to said platformstructure.
 4. The method of claim 1 wherein the step of curving saidconductor includes the step of continually curving said conductor up toapproximately 6° every 100 feet.
 5. The method of claim 1 wherein thestep of curving said conductor includes the step of pre-forming thedesired curvature in said conductor prior to the step of extending saidconductor downwardly with respect to said platform structure.
 6. Themethod of claim 1 wherein the step of extending said well conductordownwardly with respect to said platform structure includes the step ofextending the upper portion of said conductor first verticallydownwardly with respect to said platform structure, then curving saidconductor.
 7. Apparatus for producing hydrocarbons from a subterraneanhydrocarbon-bearing formation located beneath the floor of a body ofwater, said apparatus comprising:a platform structure disposed on thefloor of said body of water; at least one well conductor extendingdownwardly with respect to said platform structure, then curvedoutwardly and downwardly through said platform structure above the floorof said body of water, said conductor having a relatively smooth borethroughout substantially the entire extent thereof; a drilled wellcommunicating with both said conductor and said formation; and formationfluids recovery means associated with said conductor for recoveringformation fluids produced from said formation via said conductor.
 8. Theapparatus of claim 7 wherein said platform structure includes aplurality of conductor guide means disposed vertically thereof forcurving said conductor and said conductor engages said guide means in amanner curving said conductor.
 9. The apparatus of claim 7 including aplurality of said conductors extending downwardly with respect to saidplatform structure, at least some of said conductors extending outwardlyand downwardly with respect to said platform structure in a directiondifferent from that of an adjacent well conductor in a predeterminedpattern with respect to said platform structure.
 10. The apparatus ofclaim 7 wherein said conductor continually curves approximately up to 6°every 100 feet.
 11. The apparatus of claim 7, wherein said wellconductor extends first vertically downwardly with respect to saidplatform structure, then curves outwardly and downwardly.
 12. Theapparatus of claim 7 wherein said conductors extending downwardly withrespect to said platform structure extend below said platform structureand into the floor of said body of water. .Iadd.
 13. An anchored marinestructure at an offshore body of water adapted for directional drillingof under-water wells which comprises:a working deck positioned above thewater's surface and holding well drilling equipment; at least oneelongated leg supportably connected to said working deck and extendingdownwardly to the floor of said body of water; pile means connected tosaid structure and depending from the lower end thereof being imbeddedin the substratum of said body of water to rigidly fix said structure inplace; conductor guide means carried on said structure and being adaptedto slidably receive and deflect a drill guide conductor passeddownwardly therethrough; said conductor guide means including, discreteguide units spaced vertically apart in substantial vertical alignmentand being deviated horizontally from said substantially verticalalignment to define an arcuate center line along the common axis of saidrespective guide units. .Iaddend..Iadd.
 14. In an apparatus as definedin claim 13 including; an elongated cylindrical conductor registered insaid substantially vertically aligned discrete guide units, saidcylindrical conductor being deformed thereby into an arcuateconfiguration. .Iaddend. .Iadd.
 15. A method of installing a curved wellconductor at an offshore location having a platform structure installedon the floor of a body of water, said method comprising: extending witha downward movement at least one well conductor open at both endsdownwardly with respect to said platform structure, then curving saidconductor outwardly and downwardly through said platform structurewithin a plan view periphery thereof and above the floor of said body ofwater in a manner maintaining a relatively smooth bore throughoutsubstantially the entire extent of said conductor. .Iaddend..Iadd. 16.The method of claim 15 wherein the step of curving said conductorincludes the steps of: providing guide means at a plurality ofvertically spaced locations on said platform structure adapted to curvesaid conductor; and extending said conductor into communication withsaid guide means thereby curving said conductor through said guidemeans. .Iaddend. .Iadd.
 17. The method of claim 16 including the step ofcontinuing the extending of the curved well conductor along its curvepath and into the floor of the body of water. .Iaddend..Iadd.
 18. Themethod of claim 17 including the step of conducting well drillingoperations through said well conductor. .Iaddend..Iadd.
 19. The methodof claim 15 wherein the step of extending at least one well conductordownwardly with respect to said platform structure includes the step ofextending a plurality of well conductors downwardly with respect to saidplatform, at least some of said well conductors being extended outwardlyand downwardly with respect to said platform structure in a directiondifferent from that of an adjacent well conductor in a predeterminedpattern with respect to said platform structure. .Iaddend..Iadd.
 20. Themethod of claim 15 wherein the step of curving said conductor includesthe step of continually curving said conductor up to approximately 6°every 100 feet. .Iaddend. .Iadd.21. The method of claim 15 wherein thestep of curving said conductor includes the step of pre-forming thedesired curvature in said conductor prior to the step of extending saidconductor downwardly with respect to said platform structure. .Iaddend..Iadd.
 22. The method of claim 15 wherein the step of extending saidwell conductor downwardly with respect to said platform structureincludes the step of extending the upper portion of said conductor firstvertically downwardly with respect to said platform structure, thencurving said conductor. .Iaddend..Iadd.
 23. Apparatus for use indrilling offshore wells to increase the lateral reach of the wells, saidapparatus comprising: a platform structure disposed on the floor of abody of water; and at least one well conductor through which a well maybe drilled, said conductor extending downwardly with respect to saidplatform structure, then curved for the major portion thereof outwardlyand downwardly through said platform structure within the plan viewperiphery thereof above the floor of said body of water, said conductorhaving a relatively smooth bore throughout substantially the entireextent thereof. .Iaddend..Iadd.
 24. The apparatus of claim 23 whereinsaid platform structure includes a plurality of conductor guide meansdisposed vertically thereof within the plan view periphery of saidplatform structure for curving said conductor and said conductor engagessaid guide means in a manner curving said conductor. .Iaddend. .Iadd.25. The apparatus of claim 23 including a plurality of said wellconductors extending downwardly with respect to said platform structurewithin the plan view periphery thereof, at least some of said conductorsextending outwardly and downwardly with respect to said platformstructure in a direction different from that of an adjacent wellconductor in a predetermined pattern with respect to said platformstructure. .Iaddend..Iadd.
 26. The apparatus of claim 23 wherein saidconductor continually curves approximately up to 6° every 100 feet..Iaddend..Iadd.
 27. The apparatus of claim 23 wherein said wellconductor extends first vertically downwardly with respect to saidplatform structure, then curves outwardly and downwardly..Iaddend..Iadd.
 28. The apparatus of claim 23 wherein said wellconductors extending downwardly with respect to said platform structureextend below said platform structure and into the floor of said body ofwater. .Iaddend. .Iadd.
 29. A marine structure, adapted to be positionedon the floor of a body of water, for the directional drilling ofunderwater wells, which comprises:a substantially rigid structure of aheight, when assembled, greater than the depth of water in which saidmarine structure is to be positioned, means carried by said marinestructure for receiving anchoring means for anchoring said structure tothe floor of said body of water, and conductor pipe guide means carriedby said structure within the plan view periphery thereof to receive adrill guide conductor pipe adapted to pass downwardly therethrough alonga path the major portion of which curves outwardly and downwardlythrough said marine structure. .Iaddend..Iadd.
 30. The marine structureof claim 29 wherein said conductor pipe guide means includes a pluralityof discrete guide units spaced vertically apart and being off-sethorizontally from the vertical to define an arcuate line taken throughthe centers of successive guide means. .Iaddend.